The present invention relates in general to the field controlling fluid flow in a subterranean well and, more particularly, to a flow control device having redundant sealing capability for regulating fluid flow through a tubing string disposed within a well.
With limiting the scope of the present invention, its background will be described with reference to a regulating fluid flow into a wellbore having one or more subsea completions as an example.
In subsea completions, a flow control apparatus, known as a choke, is typically installed in the production tubing string to throttle fluid flow entering the tubing string. The choke is particularly useful where multiple zones are produced into the tubing string and it is desired to regulate the rate of fluid flow from each zone. Additionally, regulatory authorities may require that rates of production from each zone be reported, necessitating the use of the choke or other methods of determining and controlling the rate of production from each zone. Safety concerns may also dictate controlling the rate of production from each zone.
Chokes are also useful in subsea well having single zone completions. For example, in a wellbore producing from a single zone, an operator may determine that it is desirable to reduce the flow rate from that zone to limit damage to the reservoir, reduce water coning or enhance ultimate recovery.
The typical choke that is placed downhole to limit flow from a certain formation into the tubing string has a fixed orifice which cannot be closed. These conventional chokes require intervention to change the size of the fixed orifice. To compensate for changing well conditions or simply to make adjustments in the flowrate therethrough, these chokes typically require slickline, wireline or other operations, which need a rig for their performance.
Attempts have been made to overcome these limitations associated with convention chokes. For example, infinitely variable interval control valves (xe2x80x9cIVICVxe2x80x9d) have been used. These IVICVs are designed not only for operation in fully closed and fully open configurations, but also, in variable positions that allow for the regulation of fluid flow therethrough. Typically, IVICVs utilize a metal-to-metal sealing surface in the fully closed position to prevent fluid flow therethrough. It has been found, however, that the surfaces of the metal-to-metal seal are susceptible to erosion when the IVICV is in an open position, particularly when the IVICV is throttling flow. Once the sealing surfaces have been eroded, the IVICV is no longer capable of fully preventing fluid flow therethrough even when it is in the fully closed position.
Therefore a need has arisen for a flow control apparatus that is rugged, reliable, and capable of withstanding extreme environmental conditions, so that it may be utilized in completions without requiring frequent service, repair or replacement. A need has also arisen for such a flow control apparatus that is capable of accurately regulating fluid flow therethrough and that is resistant to erosion, even when it is configured between its fully open and closed positions. Further, a need has arisen for such a flow control apparatus that is capable fully providing a seal even when erosion of the metallic sealing surfaces has occurred.
The present invention disclosed herein comprises a flow regulating apparatus that is rugged, reliable and capable of withstanding extreme environmental conditions, so that it may be utilized in completions without requiring frequent service, repair or replacement. The flow regulating apparatus of the present invention is capable of accurately regulating fluid flow therethrough and is resistant to erosion, even when it is configured between its fully open and closed positions. In addition, the flow regulating apparatus of the present invention is capable of fully providing a seal even when erosion of the metallic sealing surfaces has occurred.
The flow regulating apparatus of the present invention comprises a generally tubular outer housing having a housing port formed through a sidewall portion thereof. First and second seats are disposed within the housing. The first seat is substantially fixed relative to the housing. The second seat is slidable relative to the housing. In operation, the second seat is movable relative to the first seat such that a sealing surface of the first seat and a sealing surface of the second seat may be sealingly engaged together, forming a metal-to-metal seal, to substantially prevent fluid flow therebetween. In addition, the first and second seats may be separated from one another to permit fluid flow therebetween.
The flow regulating apparatus of the present invention also comprises a sleeve that is slidably disposed within the first and second seats. The sleeve has a flow passage extending generally axially therethrough and has a sleeve port formed through a sidewall portion thereof. The sleeve is variably positionable relative to the first seat to regulate fluid flow through the sleeve port. The sleeve has a seal disposed thereon that selectively provide a redundant seal for the flow regulating apparatus of the present invention. Specifically, the seal, which may be an elastomeric seal, may be positioned between the sleeve and the first seat. In this position, the seal provides redundant sealing capability in addition to the metal-to-metal seal between the first and second seats, thereby fully preventing fluid flow between the housing port and the sleeve port of the flow regulating apparatus of the present invention.
The sleeve may be slidable repositioned relative to the first and second seats to remove the redundant sealing capability. In this position, the seal is disposed between the sleeve and the second seat. As such, the seal no longer prevents fluid flow between the housing port and the sleeve port leaving only the metal-to-metal seal to prevent fluid flow between the housing port and the sleeve port. While the metal-to-metal seal may be sufficient in some application for some period of time, typical metal-to-metal seals are susceptible to leakage, particularly if the sealing surfaces are subject to erosion. The flow regulating apparatus of the present invention, however, overcomes this limitation through the use of the redundant sealing capability provided by the seal when it is disposed between the sleeve and the first seat.
In addition, the seal of the flow regulating apparatus of the present invention is not subject to the hostile environment typically encountered in conventional choke applications. Specifically, the seal is not subject to abrasive wear or erosion either when providing or not providing the redundant seal. More specifically, the sealing surfaces of the first and second seats remain engaged during redundant sealing operations and during movement of the sleeve relative to the second seat which moves the seal out of redundant sealing operations. As such, the seal is never required to seal against high velocity fluid flow and suffer the associated degradation.
To regulate the fluid flow through the flow regulating apparatus of the present invention, the sleeve and the second seat are slidably repositionable relative to the first seat. As the sleeve continues to move in the direction that removed the redundant seal, the sleeve and the second seat begin to move together to disengage the seal between the sealing surfaces of the first and second seats. As the sleeve continues movement in this direction, the sleeve port becomes aligned with the end of the first seat such that fluid flow through the sleeve port may occur. The volume of fluid flow may now be infinitely regulated by adjusting the amount of obstruction provided by the first seat relative to the sleeve port. Continued movement of the sleeve in the original direction eventually allows unregulated fluid flow through the sleeve port when the flow regulating apparatus of the present invention is in its fully open position.
Reversing the direction of movement of the sleeve may return the flow regulating apparatus of the present invention to its fully closed position. This is achieved by first increasing the level of obstruction of the first seat relative to the sleeve port until it is fully obstructed and bringing the sealing surfaces of the first and second seats into sealing engagement with one another. Once substantially all of the fluid flow is restricted by the sealing engagement of the first and second seats, the sleeve continues its travel in this direction relative to both the first and second seats such that the seal may slide across the sealing engagement of the sealing surfaces of the first and second seats to fully seal the flow regulating apparatus of the present invention.
In one embodiment of the present invention, the movement of the sleeve relative to the first and second seats and the movement of the sleeve and second seat relative to the first seat may be achieved using mechanical means such as via wireline or slickline. In another embodiment of the present invention, the movement of the sleeve relative to the first and second seats and the movement of the sleeve and second seat relative to the first seat may be achieved using hydraulic fluid pressure.